The present invention relates to automotive lights such as headlights, fog lights, and running lights. More particularly, this invention relates to an automotive headlight in which the light which is emitted from the filament and passes by the base of the glass tube constituting the lamp bulb is shaded as far as possible in order to eliminate harmful light which is caused by upward diffusion during driving.
An automotive light should have a sufficient intensity of illumination so that any obstacle on the road ahead can be confirmed. On the other hand, an automotive light should not illuminate the opposite lane and emit upward light in order to protect the driver on a car running in the opposite direction from dazzlement. These requirements can be met for the most part by properly designing the front diffuser lens and by adjusting the angle of direction of the illuminating lamp.
It has been found that there is still a cause of problems that cannot be solved by these methods, and it consists in the structure of the lamp bulb. This will be described below.
There is one type of lamp bulb designed for improved efficiency in which the glass tube is made small, the tube is filled with a halogen gas, and radiation is accomplished at a high temperature.
In FIG. 1, plan view with a partial cutaway view, and FIG. 2, side view with a partial cutaway view, the lamp bulb (1) consists of the glass tube (2) and the filament (3) provided therein, and the base (4) of the glass tube (2) is held by the glass tube holder cylinder (5). The lamp bulb (1) is mounted at the central opening (8) of the reflector (7) through the bulb spacer (8).
This type of lamp bulb (1) has a disadvantage that it is very difficult to make the curves (9) and (10) of the base of the glass tube (2) uniform in thickness in the bulb production process. The curves (9) and (10) get thicker near the base (4), forming a prism-like structure. The range of effective luminous flux emitted from the filament (3) is usually about 290 degrees as shown in FIG. 2, and the curves (9) and (10) of the glass tube (2) are covered by this range. Thus, at these curves (9) and (10), the light from the filament (3) is deflected by the prism action. In other words, the beam of light which is supposed to pass along the chain line is deflected at the curves (9) and (10) as indicated by the solid line. This creates a condition in which the filament (3) emits light as if it had emitted light at the position (3') on the chain line, and this means that the filament is placed out of the focus. Consequently, the light which has passed through the curves (9) and (10) and has been reflected by the reflector (7) is not made parallel. The hatched parts (A) and (B) on the reflector (7) as shown in FIG. 3, which are near the center of the reflector (7) and a little lower than the horizontal line passing through the center, reflects the light upward, causing dazzlement to the driver on a car running in the opposite direction. The upward light undergoes diffused reflection in the rain, resulting in a light screen phenomenon that deteriorates driver's visibility.